Current knowledge about hypertension suggests that an elevated peripheral resistance maintains high levels of arterial blood pressure. Many observations indicate that this increase in peripheral resistance may be caused by a vasoconstriction resulting from an alteration in vascular smooth muscle which makes it more sensitive to normal stimuli. There is evidence that this increased sensitivity reflects a primary change in the membrane of vascular smooth muscle cells. The goal of this study is to characterize the functional changes that occur in the smooth muscle cell membrane in hypertension. The studies will include evaluation of the following topics: 1) functional characterization of membrane changes in vascular smooth muscle from hypertensive and normotensive animals (rats); 2) genetic aspects of functional vascular changes (spontaneously hypertensive rats); 3) determination of adrenergic influences on vascular function (rats); and 4) determination of the specificity of the vascular change (renal hypertension in rats and rabbits; mineralocorticoid hypertension in rats and pigs). The proposed experiments will be performed on isolated blood vessel segments (cerebral, coronary, mesenteric and tail arteries) from hypertensive and normotensive animals. The techniques used to evaluate vascular function include: 1) isometric recording of contractile behavior; 2) biochemical assay procedures; and 3) electron microscopic procedures. The experimental models to be investigated are: mineralocorticoid-induced hypertension, renal hypertension and genetic hypertension. It is anticipated that this study will yield important information about the functional determinants of vascular reactivity in hypertension.